I have a baxi solo 2 PF. The CH and HW are working, the pump and tank star are working. I have CH and HW. Ocasionaly the boiler goes on over heat setting. The boiler is turned down to No.2 setting. The tank stat is turned down to 50 and the pump is turned up to No.3 setting since No.2 setting was just as bad, i thought the pomp would pump the water thus pushing the water through faster and sorting the problem. When the CH heats up, the pipes bang, generally as the boiler goes off, but sometimes the boiler goes to the overheat setting. All the rads have been blead and the tank valve as well so as far as i can see there is no air in the system.